diff --git a/sphere.cpp b/sphere.cpp
index 827fc546..e8bb59be 100644
--- a/sphere.cpp
+++ b/sphere.cpp
@@ -27,6 +27,19 @@ sphere<S,T>::sphere (point<S,T> _centre, T _radius):
     CHECK_GE (_radius, 0);
 }
 
+
+//-----------------------------------------------------------------------------
+template <size_t S, typename T>
+std::ostream&
+util::operator<< (std::ostream &os, sphere<S,T> s)
+{
+    return os << "sphere(" << s.centre << ',' << s.radius << ')';
+}
+
+template std::ostream& util::operator<< (std::ostream&, sphere<2,float>);
+template std::ostream& util::operator<< (std::ostream&, sphere<3,float>);
+
+
 //-----------------------------------------------------------------------------
 template struct util::sphere<2,float>;
 template struct util::sphere<3,float>;
diff --git a/sphere.hpp b/sphere.hpp
index 2896d64d..124d691f 100644
--- a/sphere.hpp
+++ b/sphere.hpp
@@ -19,6 +19,8 @@
 
 #include "point.hpp"
 
+#include <iostream>
+
 namespace util {
     template <size_t S, typename T>
     struct sphere {
@@ -28,6 +30,9 @@ namespace util {
         T radius;
     };
 
+    template <size_t S, typename T>
+    std::ostream& operator<< (std::ostream&, sphere<S,T>);
+
     typedef sphere<2,float> sphere2f;
     typedef sphere<3,float> sphere3f;
 }